Fin mask and method for fabricating saddle type fin using the same

ABSTRACT

A fin mask for forming saddle type fins in each of active regions formed in an island shape having a certain size with a major axis and a minor axis includes a first fin mask of a line type, and a second fin mask of an island type, wherein the first fin mask and the second fin mask in combination expose saddle type fin regions and cover ends of the neighboring active regions along the major axis.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 11/679,179, filed on Feb. 26, 2007, which claims priority to Koreanpatent application numbers 10-2006-0061437 and 10-2006-0128839, filed onJun. 30, 2006 and Dec. 15, 2006, respectively, which are incorporated byreference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a method for fabricating asemiconductor device, and more particularly, to a method for fabricatinga saddle type transistor having a saddle type fin.

A typical cell in a three-dimensional structure for use in a dynamicrandom access memory (DRAM) cell includes a fin structure, a recesschannel structure, and a saddle type structure. The saddle typestructure includes the fin structure and the recess channel structure incombination.

FIG. 1A illustrates a perspective view showing a method for fabricatinga typical saddle type transistor, and FIG. 1B illustrates a plan view ofa fin mask. Referring to FIGS. 1A and 1B, an isolation structure 12 isformed in a substrate 11 using a shallow trench isolation (STI) process.Thus, an active region 11A having a major axis and a minor axis isdefined. A fin mask 13 is formed over the substrate structure. Saddletype fins 14 are formed by etching using the fin mask 13. The etchingfor forming the saddle type fins 14 may include etching the isolationstructure 12 using the fin mask 13 and then etching the active region11A, or etching the active region 11A and then etching the isolationstructure 12. The fin mask 13 is removed, and although not illustrated,a gate oxide layer, a gate electrode, and source/drain are formed tocomplete a saddle type transistor.

The typical method as described above uses the line type fin mask 13 toform the saddle type fins 14. However, in the typical method, the activeregion 11A is exposed by the line type fin mask 13 at regionspredetermined for forming the saddle type fins 14 as well as at the endsof the active region 11A along the major axis. Thus, dummy saddle typefins 14A may be formed. The dummy saddle type fins 14A may be formed inan active region that will be connected to a storage node. Thus, leakageof the storage node and capacitance of the gate may be increased,deteriorating performance of the transistor.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed towards providing afin mask and a method for fabricating a saddle type fin using the same,which can reduce formation of undesired dummy saddle type fins at theend of an active region along a major axis.

In accordance with an aspect of the present invention, there is provideda fin mask for forming saddle type fins in each of active regions formedin an island shape having a certain size with a major axis and a minoraxis, the fin mask including: a first fin mask of a line type; and asecond fin mask of an island type, wherein the first fin mask and thesecond fin mask in combination expose saddle type fin regions and coverends of the neighboring active regions along the major axis.

In accordance with another aspect of the present invention, there isprovided a fin mask for forming saddle type fins in each of activeregions formed in an island shape having a certain size with a majoraxis and a minor axis, the fin mask including: a first fin mask of aline type; and a second fin mask having openings, wherein the first finmask and the second fin mask in combination expose saddle type finregions and cover ends of the neighboring active regions along the majoraxis.

In accordance with a still another aspect of the present invention,there is provided a fin mask for forming saddle type fins in each ofactive regions formed in an island shape having a certain size with amajor axis and a minor axis, the fin mask including island-shapedopenings exposing saddle type fin regions and covering the rest of theactive regions.

In accordance with a further aspect of the present invention, there isprovided a method for fabricating a saddle type fin, including:providing a substrate defining at least two active regions that haveneighboring ends in a major axis; forming an etch barrier pattern overthe substrate, the etch barrier pattern exposing saddle type fin regionsof the active regions and covering the rest of the active regions; andetching the saddle type fin regions to form saddle type fins in a localdamascene structure, wherein forming the etch barrier pattern includesforming a first fin mask and a second fin mask, and wherein the firstfin mask exposes the saddle type fin regions in a line pattern and thesecond fin mask covers the neighboring ends of the active regions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a perspective view of a typical method forfabricating a saddle type fin.

FIG. 1B illustrates a plan view of a typical fin mask.

FIG. 2 illustrates a plan view of a fin mask combination used infabricating a saddle type fin according to a first embodiment of thepresent invention.

FIGS. 3A to 3E illustrate cross-sectional views of a method forfabricating a saddle type fin according to the first embodiment of thepresent invention.

FIG. 4 illustrates resultant saddle type fins according to the firstembodiment of the present invention.

FIG. 5A illustrates a plan view of a fin mask combination used infabricating a saddle type fin according to a second embodiment of thepresent invention.

FIG. 5B illustrates a scanning electron microscopic (SEM) view of asecond fin mask according to the second embodiment of the presentinvention.

FIG. 6A illustrates a plan view of a fin mask combination used infabricating a saddle type fin according to a third embodiment of thepresent invention.

FIG. 6B illustrates a SEM view of a second fin mask shown in FIG. 6A.

FIG. 7A illustrates a plan view of a fin mask used in fabricating asaddle type fin according to a fourth embodiment of the presentinvention.

FIG. 7B illustrates a SEM view of a fin mask shown in FIG. 7A.

FIG. 8 illustrates a SEM view of saddle type fins according toembodiments of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention relates to a fin mask and a method for fabricatinga saddle type fin using the same. Formation of dummy saddle type fins atthe ends of neighboring active regions along a major axis may be reducedthrough using a fin mask combination that locally opens saddle type finregions. Thus, leakage of the storage node and increased gatecapacitance caused by the dummy saddle type fins may be reduced.

FIG. 2 illustrates a plan view of a fin mask combination used infabricating a saddle type fin according to a first embodiment of thepresent invention. A plurality of active regions 101 are formed in asubstrate. The substrate has a flat surface with an X axis and a Y axis.The active regions 101 are formed in a certain size with a major axisand a minor axis. The active regions 101 are disposed in a manner thatends 104 along the major axis of two neighboring active regions 101along the X axis are adjacent to each other, and an isolation structure102 is formed between the adjacent active regions 101. Hereinafter, onlyone set of elements are described for convenience.

The active region 101 is defined by the isolation structure 102. Forminga fin mask according to the first embodiment includes using a first finmask FM1 and a second fin mask FM2 in combination to form saddle typefins 103. The active region 101 and the isolation structure 102 areselectively etched to form the saddle type fins 103, that is, the activeregion 101 protruding in a saddle type structure. In the presentembodiment, the first fin mask FM1 and the second fin mask FM2 may besequentially used according to a given order, and the given order may bechangeable. For instance, the first fin mask FM1 may be formed first andthe second fin mask FM2 may be formed after the first fin mask FM1 isremoved. On the other hand, the second fin mask FM2 may be formed firstand the first fin mask FM1 may be formed after the second fin mask FM2is removed. However, FIG. 2 illustrates both the first and second finmasks FM1 and FM2 together to show the relative position of the firstand second fin masks FM1 and FM2.

The first fin mask FM1 is a line type mask that is formed along a firstdirection, and the second fin mask FM2 is an island type mask that isformed along a second direction that is orthogonal to the firstdirection. Using the first fin mask FM1 and the second fin mask FM2 incombination allows selectively etching portions of the active region 101and the isolation structure 102 predetermined for forming the saddletype fins 103. That is, portions where dummy saddle type fins usuallyoccur (i.e., the ends 104 along the major axis of two neighboring activeregions 101 along the X axis) are not etched during an etching processfor forming the saddle type fins 103. This result may be obtainedbecause the island type second fin mask FM2 is applied.

For instance, the second fin mask FM2 may be an island type mask of arectangular shape formed to cover the ends 104 along the major axis ofthe neighboring active regions 101 and cover the isolation structure 102between the two active regions 101. The second fin mask FM2 is formed atleast partly to intersect the location where the first fin mask FM1 wasformed. The first fin mask FM1 and the second fin mask FM2 may beapplied in a certain order. A hard mask pattern transcribing the shapeof the first fin mask FM1 and the second fin mask FM2 in combination isused as an etch barrier when forming the saddle type fins 103.

FIGS. 3A to 3E illustrate cross-sectional views of a method forfabricating a saddle type fin according to the first embodiment of thepresent invention.

Referring to FIG. 3A, an isolation structure 24 is formed in a substrate21 using a shallow trench isolation (STI) process. The isolationstructure 24 defines an active region 21A. A pad oxide layer 22 and apad nitride layer 23 are formed over the active region 21A. In moredetail, the STI process includes forming an oxide-based layer and anitride-based layer over the substrate 21 in sequential order whenforming the isolation structure 24. An etching process is performed toform trenches in the substrate 21 using an STI mask. The STI mask isremoved. An insulation layer (e.g., a high density plasma (HDP) oxidelayer) is filled in the trenches, and a chemical mechanical polishing(CMP) process is performed. Consequently, the pad oxide layer 22 and thepad nitride layer 23 are formed over the active region 21A after the CMPprocess is performed. The active region 21A includes an island typepattern having a major axis and a minor axis. In a plan view, the activeregion 21A has substantially the same shape and layout as the activeregions 101 shown in FIG. 2.

An amorphous carbon layer 25, a dielectric anti-reflective coating(DARC) layer 26, a polysilicon hard mask 27, and a first patternedbottom anti-reflective coating (BARC) layer 28A are formed over theresulting substrate structure. In more detail, the amorphous carbonlayer 25, the DARC layer 26, a polysilicon hard mask layer, and a firstBARC layer are formed over the substrate structure. The selectivitybetween the DARC layer 26 and the amorphous carbon layer 25 isapproximately 10:1 or higher. Thus, the DARC layer 26 functions as ahard mask when etching the amorphous carbon layer 25. The polysiliconhard mask layer functions as a hard mask when etching the DARC layer 26.Both the DARC layer 26 and the polysilicon hard mask layer may have athickness of approximately 1,000 Å or less. The amorphous carbon layer25 may be used as a hard mask for forming a subsequent saddle type fin.The amorphous carbon layer 25 may have a thickness of approximately 500Å or greater.

A first fin mask (FM1) 29 is formed over the first BARC layer. The FM129 includes a photoresist layer patterned by a photo-exposure anddeveloping process. The FM1 29 includes line type first openings 29Aexposing saddle type fin regions. That is, the FM1 29 is formed in aline mask shape, wherein the first openings 29A are formed to intersectwith the major axis of the active region 21A. The active region 21A andthe FM1 29 are disposed in substantially the same manner as the activeregions 101 and the first fin mask FM1 shown in FIG. 2.

An etching process is performed to etch the first BARC layer and thepolysilicon hard mask layer using the FM1 29 as an etch mask.Consequently, the first patterned BARC layer 28A and the polysiliconhard mask 27 are formed. Thus, the polysilicon hard mask 27 is formed ina line type pattern, transcribing the shape of the FM1 29.

Referring to FIG. 3B, the FM1 29 is removed. The first patterned BARClayer 28A is also removed at this time. A second BARC layer 28B isformed over the resultant substrate structure. A second fin mask (FM2)30 is formed over the second BARC layer 28B. The FM2 30 includes aphotoresist layer patterned by a photo-exposure and developing process.In a plan view, the FM2 30 covers the ends of two neighboring activeregions 21A along the major axis. Thus, the FM2 30 exposes the saddletype fin regions through a second opening 30A, and yet covers the endsof the active regions 21A along the major axis where the dummy saddletype fins may form and the isolation structure 24 formed between theends. The FM2 30 is formed in an island shape. Thus, the FM2 30 and theFM1 29 are shaped differently.

Referring to FIG. 3C, an etching process is performed using the FM2 30as an etch mask. That is, the second BARC layer 28B and the DARC layer26 are etched to form a patterned second BARC layer 28C and a patternedDARC layer 26A. At this time, the polysilicon hard mask 27 may not beetched. Thus, the DARC layer 26 below the polysilicon hard mask 27 isetched in a manner such that the patterned DARC layer 26A isself-aligned by the polysilicon hard mask 27. Referring to FIG. 3D, theFM2 30 is removed. The patterned second BARC layer 28C is also removedat this time.

Referring to FIG. 3E, the polysilicon hard mask 27 is removed. Theamorphous carbon layer 25 is etched to form an amorphous carbon pattern25A using the patterned DARC layer 26A as a mask. A plan view of theamorphous carbon pattern 25A transcribing the shape of the patternedDARC layer 26A is shown in FIG. 4. The pad nitride layer 23 and the padoxide layer 22 are etched to form a patterned pad nitride layer 23A anda pad oxide layer 22A. The isolation structure 24 and the active region21A are then selectively recessed to form saddle type fins 31. Referencenumeral 24A represents recessed portions of the isolation structure 24.The patterned DARC layer 26A is etched away when forming the saddle typefins 31. The amorphous carbon pattern 25A functions as an etch barrier.

The amorphous carbon pattern 25A prevents the etching of the ends of twoneighboring active regions 21A along the major axis when forming thesaddle type fins 31. Consequently, only the saddle type fin regions(refer to line B-B′) of the active region 21A and the isolationstructure 24 are etched. The active regions 21A and the isolationstructure 24 at the ends of the active regions 21A along the major axiswhere the dummy saddle type fins often occur may not be etched. Theresultant saddle type fins 31 are described in a plan view in FIG. 4.

FIG. 4 illustrates the resultant saddle type fins according to the firstembodiment of the present invention. The amorphous carbon pattern 25Aformed by the combination of the FM1 29 and the FM2 30 exposes thesaddle type fin regions (refer to line B-B′) of the active regions 21Awith rectangular type openings 100A. The amorphous carbon pattern 25Acovers regions where dummy saddle type fins often occur as denoted withreference numeral 100B.

Accordingly, forming the saddle type fins 31 by etching using theamorphous carbon pattern 25A reduces the etching of the ends of theactive regions 21A along the major axis. Thus, the dummy saddle typefins are not formed. The saddle type fin regions to be etched aredefined in a rectangular shape by the rectangular type openings 100A andare locally etched. Thus, the saddle type fins 31 according to the firstembodiment may be referred to as local damascene saddle type fins(LD-SF).

In the aforementioned first embodiment, the line type FM1 29 is usedbefore using the island type FM2 30. However, an amorphous carbonpattern having substantially the same shape as the one shown in FIG. 4may be obtained even when the island type FM2 30 is used before usingthe line type FM1 29.

FIG. 5A illustrates a plan view of a fin mask combination used infabricating a saddle type fin according to a second embodiment of thepresent invention. A second fin mask (FM21) of the fin mask combinationaccording to the second embodiment has a shape different from the secondfin mask (FM2) according to the first embodiment.

A plurality of active regions 111 are formed in a substrate. Thesubstrate has a flat surface with an X axis and a Y axis. The activeregions 111 are formed in a particular size with a major axis and aminor axis. The active regions 111 are disposed in a manner that theends 114 along the major axis of two neighboring active regions 111along the X axis are adjacent to each other, and an isolation structure112 is formed between the adjacent active regions 111. Hereinafter, onlyone set of elements are described for convenience.

The active region 111 is defined by the isolation structure 112. Forminga fin mask according to the second embodiment includes using a first finmask FM11 and a second fin mask FM21 in combination to form saddle typefins 113. The active region 111 and the isolation structure 112 areselectively etched to form the saddle type fins 113, that is, the activeregion 111 protruding in a saddle type structure. In the presentembodiment, the first fin mask FM11 and the second fin mask FM21 may besequentially used according to a given order, and the given order may bechangeable. For instance, the first fin mask FM11 may be formed firstand the second fin mask FM21 may be formed after the first fin mask FM11is removed. On the other hand, the second fin mask FM21 may be formedfirst and the first fin mask FM11 may be formed after the second finmask FM21 is removed. However, FIG. 5A illustrates both the first andsecond fin masks FM11 and FM21 together to show the relative position ofthe first and second fin masks FM11 and FM21.

The first fin mask FM11 is a line type mask that is formed along a firstdirection, and the second fin mask FM21 is an island type mask that isformed along a second direction that is orthogonal to the firstdirection. The saddle type fin regions of the active region 111 and theisolation structure 112, where the saddle type fins 113 are to beformed, may be locally etched by combining the two fin masks. That is,portions where dummy saddle type fins usually occur (i.e., the ends 114along the major axis of two neighboring active regions 111 along the Xaxis) are not etched during an etching process for forming the saddletype fins 113. This result may be obtained because the island typesecond fin mask FM21 is applied.

For instance, the second fin mask FM21 may be a dumbbell-shaped islandtype mask formed to cover the ends 114 along the major axis of theneighboring active regions 111 and cover the isolation structure 112between the two active regions 111. The dumbbell-shaped island type maskincludes a rectangular shape over the isolation structure 112 betweenthe neighboring active regions 111. The dumbbell-shaped island type maskalso includes a ball or an ellipse shape over the ends 114 of eachactive region 111 such that the dumbbell-shaped island type mask coversthe ends 114 with an increased surface area. The second fin mask FM21 isformed to intersect at least partly the location where the first finmask FM11 was formed.

The second fin mask FM21 is formed as the dumbbell-shaped island typemask according to the second embodiment unlike the second fin mask FM2that is formed as a rectangular island type mask according to the firstembodiment. Using the second fin mask FM21 of the dumbbell-shaped islandtype may increase the margin for covering the ends 114 of the activeregion 111. That is, the margin for reducing the chances of dummy saddletype fin generation at the ends 114 of the active region 111 mayincrease.

The first fin mask FM11 and the second fin mask FM21 may be applied in acertain order (i.e., FM11→FM21 or FM21→FM11). A hard mask patterntranscribing the shape of the first fin mask FM11 and the second finmask FM21 in combination is used as an etch barrier when forming thesaddle type fins 113. The etch barrier may include an amorphous carbonpattern. The amorphous carbon pattern may be formed by employing thefirst fin mask FM11, the second fin mask FM21, a DARC layer, and apolysilicon hard mask. The amorphous carbon pattern may be formed usingthe method shown in FIGS. 3A to 3E. FIG. 5B illustrates a scanningelectron microscopic (SEM) view of a second fin mask according to thesecond embodiment of the present invention.

FIG. 6A illustrates a plan view of a fin mask combination used infabricating a saddle type fin according to a third embodiment of thepresent invention. The fin mask combination according to the thirdembodiment includes a first fin mask FM31 of a line type and a secondfin mask FM32 of a jigsaw puzzle type for locally etching active regions200 and an isolation structure to form saddle type fins 201.

The first fin mask FM31 is a line type mask exposing only the saddletype fin regions of the active regions 200, where the saddle type fins201 are to be formed. The first fin mask FM31 is substantially the sameas the first fin masks according to the first and second embodiments.The second fin mask FM32 is a jigsaw puzzle type mask. That is, thesecond fin mask FM32 having the jigsaw puzzle shape covers ends of theactive regions 200 along a major axis as well as between the ends.Meanwhile, the second fin mask FM32 exposes the rest of the substratestructure through jigsaw puzzle openings 202. Regions exposed by thejigsaw puzzle openings 202 are locally etched to form the saddle typefins 201.

Using the second fin mask FM32 of jigsaw puzzle type according to thethird embodiment may allow the selectivity of a photoresist layer to bemaintained, which may otherwise be insufficient. Thus, the ends of theactive regions 200 along the major axis where dummy saddle type finsoften occur may be sufficiently covered.

The first fin mask FM31 and the second fin mask FM32 are applied in acertain order (i.e., FM31→FM32 or FM32→FM31). A hard mask patterntranscribing the shape of the first fin mask FM31 and the second finmask FM32 in combination is used as an etch barrier pattern when formingthe saddle type fins 201. The etch barrier pattern may include anamorphous carbon pattern. The amorphous carbon pattern may be formed byemploying the first fin mask FM31, the second fin mask FM32, a DARClayer, and a polysilicon hard mask. The amorphous carbon pattern may beformed using the method shown in FIGS. 3A to 3E. FIG. 6B illustrates aSEM view of the second fin mask shown in FIG. 6A.

FIG. 7A illustrates a plan view of a fin mask used in fabricating asaddle type fin according to a fourth embodiment of the presentinvention. FIG. 7B illustrates a SEM view of the fin mask shown in FIG.7A.

Referring to FIG. 7A, unlike the first to third embodiments, a fin maskR-FM having island-shaped openings 302 is used independently withoutusing a line type first fin mask. That is, the fin mask R-FM having theopenings 302 locally exposes saddle type fin regions of active regions300, where saddle type fins 301 are to be formed. The rest of thesubstrate structure is covered by the fin mask R-FM. The openings 302may have a rectangular shape as illustrated or an elliptical shape.

Using the fin mask R-FM having the island-shaped openings 302independently may simplify the process when compared to using two finmasks. Also, using the fin mask R-FM according to the fourth embodimentgenerally does not require using a polysilicon hard mask. The saddletype fins 301 may be formed using only amorphous carbon. The saddle typefins 301 may include polysilicon instead of amorphous carbon. Therefore,a hard mask stack may be simply configured using the fin mask R-FMaccording to the fourth embodiment. For instance, an etch barrierpattern transcribing the shape of the fin mask R-FM is used as an etchbarrier when forming the saddle type fins 301 using the fin mask R-FMaccording to the fourth embodiment. The etch barrier pattern may includean amorphous carbon pattern or a poylsilicon pattern. The etch barrierpattern may be formed by employing the fin mask R-FM and a DARC layer.The etch barrier pattern may be formed using the method shown in FIGS.3A to 3E. According to the fourth embodiment, the DARC layer may bedirectly etched using the fin mask R-FM without using the polysiliconhard mask, and the amorphous carbon may be etched using the DARC layer.Also, polysilicon may be used as an etch barrier when forming the saddletype fins by forming polysilicon under the DARC layer instead ofamorphous carbon.

Saddle type fins may be formed in a local damascene form when the saddletype fins are formed using the fin mask combination or the independentfin mask R-FM according to the first to the fourth embodiments. Sincethe saddle type fin regions are limited and locally etched, the saddletype fins become local damascene saddle type fins (LD-SF). FIG. 8illustrates a SEM view of saddle type fins according to embodiments ofthe present invention. The saddle type fins are formed as representedwith ‘LD-SF.’

While the present invention has been described with respect to specificembodiments, it will be apparent to those skilled in the art thatvarious changes and modifications may be made without departing from thespirit and scope of the invention as defined in the following claims.

1. A fin mask for forming saddle type fins in each of active regionsformed in an island shape having a certain size with a major axis and aminor axis, the fin mask comprising: a first fin mask of a line type;and a second fin mask having openings, wherein the first fin mask andthe second fin mask in combination expose saddle type fin regions andcover ends of the neighboring active regions along the major axis. 2.The fin mask of claim 1, wherein the openings of the second fin mask areformed in an island shape, the island shape including a jigsaw puzzleshape.
 3. A method for fabricating a saddle type fin, the methodcomprising: providing a substrate defining at least two active regionsthat have neighboring ends in a major axis; forming an etch barrierpattern comprising a first fin mask and a second fin mask over thesubstrate, wherein the first fin mask exposes saddle type fin regions ina line pattern, and wherein the second fin mask covers the neighboringends of the active regions and exposes the saddle type fin regions in anisland pattern comprising a jigsaw puzzle shape; and etching the saddletype fin regions to form saddle type fins in a local damascenestructure.
 4. The method of claim 3, wherein forming the etch barrierpattern comprises forming an amorphous carbon pattern.
 5. The method ofclaim 4, wherein forming the amorphous carbon pattern comprises: formingan amorphous carbon layer; forming a dielectric anti-reflective coating(DARC) layer over the amorphous carbon layer; forming a polysiliconlayer over the DARC layer; etching the polysilicon layer using the firstfin mask; etching the DARC layer using the second fin mask; and etchingthe amorphous carbon layer using the DARC layer.
 6. The method of claim4, wherein forming the amorphous carbon pattern comprises: forming anamorphous carbon layer; forming a dielectric anti-reflective coating(DARC) layer over the amorphous carbon layer; forming a polysiliconlayer over the DARC layer; etching the polysilicon layer using thesecond fin mask; etching the DARC layer using the first fin mask; andetching the amorphous carbon layer using the DARC layer.